The subject matter disclosed herein relates to industrial control systems and, in particular, to a method and system for providing a modular backplane in an industrial controller for scalability and configurability.
Industrial controllers, such as programmable logic controllers (PLC's) or programmable activity controllers (PAC's), are specialized electronic computer systems used for the control of industrial machines or processes, for example, in a factory environment. Industrial controllers differ from conventional computers in a number of ways. Physically, they are constructed to be substantially more robust against shock and damage and to better resist external contaminants. The industrial controllers perform real-time control and execute languages allowing ready customization of programs to comport with a variety of different controller applications. Industrial controllers may have a user interface for accessing, controlling and/or monitoring the industrial controller, such as through a locally connected terminal having a keyboard, mouse and display.
As is known to those skilled in the art, industrial controllers are configurable according to the requirements of the controlled machine or process. The industrial controller includes a processor module and various input and output modules. The input modules receive signals from sensors, switches, and other devices providing the operating status of the controlled machine or process. The processor module executes a control program which receives the input signals and generates output signals in response to the operating status of the controlled machine or process. The output signals are delivered from the output modules to actuators, indicators, and other devices to achieve a desired operation of the controlled machine or process. Still other modules, such as a counter module, network module, and the like may be included in the controlled machine or process.
In order to receive input signals from and provide output signals to various modules, the processor module must communicate with each module. Typically, a dedicated communication bus, also known as a backplane, is provided between the processor module and each additional module connected to the processor module. The backplane is configured to accommodate high-speed and reliable communications between modules. Additionally, because the bus is a dedicated bus configured to communicate between known modules, communication can occur in a predefined format, such as a proprietary communication protocol or utilizing a predefined communication schedule that requires little or no data overhead, such as headers, footers, checksums, and the like. However, each module must utilize the same protocol and be configured to communicate according to the predefined format on the backplane.
Typically, a backplane is configured in a linear, or daisy-chain, format. Modules are mounted in a rack or otherwise mounted adjacent to each other and data is transmitted between adjacent modules. A linear configuration, however, is not without certain drawbacks. If one module is removed from the system, the chain is broken and modules cannot communicate with modules beyond the open slot.
Thus, it would be desirable to provide an industrial controller with a linear backplane that maintains communication between modules when one module fails or is removed.
In certain applications, such as a safety application or a high-reliability application, the industrial controller may be configured to use redundant devices and/or redundant communication busses to achieve a desired a safety rating or a desired operational reliability for the application. In such an application, the industrial controller may include two processor modules, pairs of input modules, pairs of output modules, and dual communication paths between each of the modules. Adding the redundant configuration is not without certain drawbacks. When an industrial controller is configured in the redundant configuration, every module is duplicated increasing hardware expense as well as installation and commissioning expense. In addition, if a user wishes to upgrade an existing system, the existing hardware needs to be removed and replaced.
In certain applications, however, it would be desirable to provide an industrial controller which can provide a range of capability, including simple, general applications, high reliability applications, or a combination thereof. Thus, it would be desirable to provide a modular industrial controller that permits flexible configuration and interconnection between different types of modules and that also simplifies upgrades of existing systems.